The long-term goal of this project is to understand the functional roles of a newly identified growth/differentiation factor, pleiotrophin (PTN) in vivo. This work is very important both to understand cell growth and differentiation in normal angiogenesis, in abnormal proliferative responses in blood vessel walls, and in tissue repair, as well as to understand the development disorders in the nervous system, bone, and in tumor formation. Previous work indicates that PTN is a developmentally regulated protein with extraordinary conservation among mammalian species and with mitogenic and neurite outgrowth activities. It is highly expressed in the nervous system, particularly in the ventricular zones of the brain, a site of active angiogenesis. It is mitogenic towards brain capillary endothelial cells and angiogenic in the cornea transfection of its cDNA into fibroblasts results in cell transformation and induces highly vascularized tumors in nude mice. Ptn is also highly expressed in human malignant tumors, such as neuroblastoma, Wilm's tumors, breast carcinoma, osteosarcoma, and melanoma, which later also is highly vascularized. In order to study the regulation of Ptn gene in normal and abnormal cells with angiogenesis and oncogenesis in vivo, we propose first to isolate murine Ptn gene by molecular cloning and sequencing, and to characterize the structure of Ptn gene. It is then planned to inactivate the murine Ptn gene in vivo via homologous recombination and to define the phenotype of a mouse that does not express the Ptn gene product. The results of this study will provide a clear understanding of the functional role of PTN in vivo , particularly in the development of blood vessels, nervous system, and bone formation as well as clear information concerning the molecular basis of regulation of the Ptn gene. The information obtained in this project should provide a clearer knowledge of physiologic and pathologic phenomena to the human diseases.